1. Field of the Invention
The present invention relates to a vehicle surroundings monitoring apparatus which detects an object existing around a vehicle using an image captured by a camera, a vehicle surroundings monitoring method therefor, a vehicle equipped with the vehicle surroundings monitoring apparatus, and a vehicle surroundings monitoring program for use in the vehicle surroundings monitoring apparatus.
2. Description of Related Art
The applicant of the present application suggested an apparatus which monitors the surroundings of a vehicle based on an image captured by a camera mounted on the vehicle as disclosed, for example, in Japanese Patent Laid-Open No. 2003-284057 (hereinafter, referred to as Patent Document 1) or U.S. Pat. No. 7,130,448B2 (hereinafter, referred to as Patent Document 2).
In the technologies disclosed in Patent Documents 1 and 2, two infrared cameras capture images in front of the vehicle and an object is extracted from one of the two captured images. Thereafter, the real space position of the object with respect to the vehicle is detected on the basis of a parallax between the two captured images of the extracted object. Furthermore, determinations are made on a moving direction of the object recognized based on the real space position of the extracted object and time-series data of the object, and an object type (whether a person or an artificial structure). According to the determination results, it is determined whether the object should be considered as a warning target (whether the object is the object which must be avoided from coming into contact with the vehicle). In the case where it is determined to be considered as a warning target, a warning by a sound or an image is issued to a driver. The object type is determined for an object existing approximately in the area in front of the vehicle (the area slightly wider than the vehicle width). In addition, the moving direction of the object is determined for an object existing outside the area.
In the meantime, the object that can be extracted from the image captured by a camera such as an infrared camera includes various types of bodies other than a person such as, for example, an animal, another vehicle, a tree, a utility pole, and a vending machine as well as the person. Among these objects, an object which must be avoided from coming into contact with the vehicle is a person or an animal (a living body) including a person. Therefore, it is required to determine the type of the object extracted from the captured image with a distinction between a living body including a person and any other type (artificial structure).
On the other hand, in Patent Documents 1 and 2, whether the object is likely to be a person (pedestrian) is determined based on various feature values (the luminance distribution, shape, size, and the like) of the image of the object (partial image corresponding to the object) in the captured image. In this instance, an object other than a pedestrian may be determined to be likely to be a pedestrian. Therefore, whether the object is an artificial structure is determined by further determining whether the shape of the partial image of the object matches a predetermined registered pattern of an artificial structure or whether the partial image has a right-angle portion or a linear edge (by further determining whether the partial image of the object has a feature that generally cannot be found in a pedestrian). In the case where the object is determined to be likely to be a pedestrian and not to be an artificial structure as a result of the above determinations, the object is determined to be a pedestrian. The above determination process enables the determination of whether the object is a pedestrian (person) or any other type of object such as an artificial structure with high reliability.
On the other hand, the technologies disclosed in Patent Documents 1 and 2 requires calculations of various feature values or determination processes on the feature values for the object type is determined with the distinction between a pedestrian and any other type. In addition, they require the determination of whether the object is an artificial structure. It is because only the feature values employed in the technologies of Patent Documents 1 and 2 are insufficient to make a distinction between a pedestrian and any other type of object with high reliability. Furthermore, in the case where an object to be avoided is a living body including not only a pedestrian but other types of animals (dogs, cats, and other animals that can move on the ground), it is still necessary to determine whether the object belongs to one of these other types of animals.
Therefore, it has been desired to develop a technique for easily determining the object with a distinction between a living body such as a pedestrian and any other type with high reliability.
Furthermore, in the technologies disclosed in Patent Documents 1 and 2, particularly in the case where a lot of objects are extracted from the captured image, it is necessary to perform arithmetic processing for calculating various feature values and determination processes on the feature values for each of these objects. For this reason, in the technologies disclosed in Patent Documents 1 and 2, a large load is imposed on the arithmetic processing for definitely determining whether the object is a pedestrian and it has been desired to reduce the load.